From c1e7edabc1dfbe387546297720fc495837d38d33 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Matteo=20Gm=C3=BCr?= <matteo.gmuer1@ost.ch>
Date: Sun, 1 Dec 2024 09:46:37 +0000
Subject: Fix guard page and ensure it crashes even if guard page is skipped
 altogether

---
 arch/x86_64/src/boot/boot.s     | 16 ++++++++++------
 arch/x86_64/src/kernel/main.cpp | 35 ++++++++++++++++++++++++-----------
 2 files changed, 34 insertions(+), 17 deletions(-)

(limited to 'arch/x86_64/src')

diff --git a/arch/x86_64/src/boot/boot.s b/arch/x86_64/src/boot/boot.s
index c1b3203..8d27ea1 100644
--- a/arch/x86_64/src/boot/boot.s
+++ b/arch/x86_64/src/boot/boot.s
@@ -7,6 +7,16 @@
  * Uninitialized data for the bootstrapping process.
  */
 .section .boot_bss, "aw", @nobits
+
+/**
+ * Reserve some space for the Multiboot 2 information pointer.
+ */
+.global multiboot_information_pointer
+multiboot_information_pointer: .skip 4
+
+/**
+ * Align page maps to 4 KiB or the assembler code, will cause crashes when attempting to enable paging.
+ */
 .align 4096
 
 /**
@@ -30,12 +40,6 @@ page_map_level_3: .skip 512 * 8
 .global page_map_level_2
 page_map_level_2: .skip 512 * 8
 
-/**
- * Reserve some space for the Multiboot 2 information pointer.
- */
-.global multiboot_information_pointer
-multiboot_information_pointer: .skip 4
-
 /**
  * Stack space for the bootstrapping process.
  *
diff --git a/arch/x86_64/src/kernel/main.cpp b/arch/x86_64/src/kernel/main.cpp
index dd0a1d8..7463fc4 100644
--- a/arch/x86_64/src/kernel/main.cpp
+++ b/arch/x86_64/src/kernel/main.cpp
@@ -8,14 +8,19 @@
 
 namespace teachos::arch::kernel
 {
-  auto main() -> void
+  auto stack_overflow_test(int count) -> int
   {
-    video::vga::text::clear();
-    video::vga::text::cursor(false);
-    video::vga::text::write("TeachOS is starting up...", video::vga::text::common_attributes::green_on_black);
-
-    memory::initialize_memory_management();
+    int test[5000] = {};
+    if (test[0] == 0xFFFF)
+    {
+      return count;
+    }
+    count = stack_overflow_test(count);
+    return count++;
+  }
 
+  auto heap_test() -> void
+  {
     memory::heap::bump_allocator heap_allocator{memory::heap::HEAP_START,
                                                 memory::heap::HEAP_START + memory::heap::HEAP_SIZE};
     auto test = heap_allocator.allocate(1024);
@@ -28,14 +33,22 @@ namespace teachos::arch::kernel
     test5.kernel_end = 3000;
     auto test6 = test4.kernel_end;
     auto test7 = test5.kernel_end;
-    if (test6 && test7)
+    auto test8 = memory::multiboot::read_multiboot2();
+    if (test6 && test7 && test8.kernel_end)
     {
       video::vga::text::write("Kernel remapping successfull", video::vga::text::common_attributes::green_on_black);
     }
+  }
+
+  auto main() -> void
+  {
+    video::vga::text::clear();
+    video::vga::text::cursor(false);
+    video::vga::text::write("TeachOS is starting up...", video::vga::text::common_attributes::green_on_black);
+
+    memory::initialize_memory_management();
 
-    // TODO: Why is identity mapping multiboot2 information structure with new kernel not required and
-    // allocator.allocate_frame still works?
-    // TODO: Fix unmapping old level 4 page table and turn it into guard page, use Stack Probes for stack allocation if
-    // possible.
+    // stack_overflow_test(0);
+    // heap_test();
   }
 }  // namespace teachos::arch::kernel
-- 
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